Final Engineering services report _62 Lake Macdonald Drive · OPW25/0057

The basin is sized suitably to meet the water quality requirements identified in the following sections. The bioretention
basin is not designed as a water quantity (detention) device, detention requirement is to be determined and provided
on a lot-by-lot basis to suit the proposed future built forms.

The bioretention basin outlet pipe system is sized to direct flow from the 10 % AEP event into the existing Council
piped network. The existing Council network in turn, caters for the 10 % AEP flows.

For less frequent rainfall events, flows above the 10 % AEP will outlet the bioretention basin through the overflow
weir.

3.9.1   Water Quality and Treatment Objectives

This section will demonstrate how the proposed stormwater quality management strategy complies with the
requirements of the Noosa Plan (2020) and the SPP (2017) in terms of demonstrating how the relevant stormwater
pollutant reduction objectives will be met.

Stormwater runoff generated from the site must achieve the required pollutant reduction targets and be
demonstrated in MUSIC. Table 2: Pollutant Reduction Targets for South East Queensland quantifies the reduction
objectives required under the NSC Water Quality and Drainage Code (NSC, 2020) and the Queensland State Planning
Policy (SPP, 2017).
Table 2: Pollutant Reduction Targets for South East Queensland
                   Pollutant Type                                             Reduction Objective
            Total Suspended Solids (TSS)                        80% reduction in average annual load of pollutants
               Total Phosphorus (TP)                            60% reduction in average annual load of pollutants
                Total Nitrogen (TN)                             45% reduction in average annual load of pollutants
               Gross Pollutants (GP)                            90% reduction in average annual load of pollutants

3.9.2   Catchment Description

The development site will be divided into three (3) lots and one (1) balance lot, including road reserve and drainage
reserve. The proposed drainage reserve will contain a bioretention basin which will exclusively treat Catchment A as
shown in Figure 6.

Catchment A:

The proposed treated Catchment A includes Lots 1 and 2, the proposed road reserve areas which drain to the
bioretention basin in lot 900. Ultimately, this yields the total treatable area of 1.66 ha in the associated MUSIC model.

Catchment B:

The developer of Lot 3 is to ensure its stormwater treatment independently complies with the relevant stormwater
quality guidelines. Any future stormwater treatment infrastructure proposed for Lot 3 is to be contained within the
allotment. It is assumed that a stormwater treatment area will be provided in the lower (southern) corner of the site.
An outlet pipe will be provided as a point of discharge.

Catchment C:

This catchment encompasses the balance lot which is to remain unchanged with no stormwater treatment proposed.




62 Lake Macdonald Drive, Cooroy – Engineering Services Report                                                        Page 8
233467 | M24-1037Rpt – Issue A – April 2025